We here encounter a great difficulty. How can the contraction of
the unstriped and involuntary _arrectores pili_ have been co-ordinated
with that of various voluntary muscles for the same special purpose?
If we could believe that the arrectores primordially had been
voluntary muscles, and had since lost their stripes and become involuntary,
the case would be comparatively simple. I am not, however, aware that
there is any evidence in favour of this view; although the reversed
transition would not have presented any great difficulty,
as the voluntary muscles are in an unstriped condition in the embryos
of the higher animals, and in the larvae of some crustaceans.
Moreover in the deeper layers of the skin of adult birds, the muscular
network is, according to Leydig,[20] in a transitional condition;
the fibres exhibiting only indications of transverse striation.

Another explanation seems possible. We may admit that originally
the _arrectores pili_ were slightly acted on in a direct manner,
under the influence of rage and terror, by the disturbance
of the nervous system; as is undoubtedly the case with our
so-called _goose-skin_ before a fever-fit. Animals have been
repeatedly excited by rage and terror during many generations;
and consequently the direct effects of the disturbed nervous
system on the dermal appendages will almost certainly
have been increased through habit and through the tendency
of nerve-force to pass readily along accustomed channels.
We shall find this view of the force of habit strikingly
confirmed in a future chapter, where it will be shown that
the hair of the insane is affected in an extraordinary manner,
owing to their repeated accesses of fury and terror.
As soon as with animals the power of erection had thus been
strengthened or increased, they must often have seen the hairs
or feathers erected in rival and enraged males, and the bulk
of their bodies thus increased. In this case it appears possible
that they might have wished to make themselves appear larger
and more terrible to their enemies, by voluntarily assuming
a threatening attitude and uttering harsh cries; such attitudes
and utterances after a time becoming through habit instinctive.
In this manner actions performed by the contraction
of voluntary muscles might have been combined for the same
special purpose with those effected by involuntary muscles.
It is even possible that animals, when excited and dimly
conscious of some change in the state of their hair, might act
on it by repeated exertions of their attention and will;
for we have reason to believe that the will is able to
influence in an obscure manner the action of some unstriped
or involuntary muscles, as in the period of the peristaltic
movements of the intestines, and in the contraction of the bladder.
Nor must we overlook the part which variation and natural
selection may have played; for the males which succeeded
in making themselves appear the most terrible to their rivals,
or to their other enemies, if not of overwhelming power,
will on an average have left more offspring to inherit their
characteristic qualities, whatever these may be and however
first acquired, than have other males.

[20] `Lehrbuch der Histologie,' 1857, s. 82.

_The inflation of the body, and other means of exciting fear
in an enemy_.--Certain Amphibians and Reptiles, which either have
no spines to erect, or no muscles by which they can be erected,
enlarge themselves when alarmed or angry by inhaling air.
This is well known to be the case with toads and frogs.
The latter animal is made, in AEsop's fable of the `Ox and the Frog,'
to blow itself up from vanity and envy until it burst.
This action must have been observed during the most ancient times, as,
according to Mr. Hensleigh Wedgwood,[21] the word _toad_ expresses
in all the languages of Europe the habit of swelling. It has been
observed with some of the exotic species in the Zoological Gardens;
and Dr. Gunther believes that it is general throughout the group.
Judging from analogy, the primary purpose probably was to make the body
appear as large and frightful as possible to an enemy; but another,
and perhaps more important secondary advantage is thus gained.
When frogs are seized by snakes, which are their chief enemies,
they enlarge themselves wonderfully; so that if the snake be of
small size, as Dr.